Last month we were aboard the Carnival Liberty and had 2 port holes. No, you couldn't open them but they did have heavy covers that you could close if you wanted your room completely dark.
A little sign was posted under them informing us to "close the port hole covers (to block out the light) during the night so not to interfere with the navigational system". ????huh With our big modern and sophisticated ships now, this could really cause a problem?
Maybe some of our retired Navy can explain this to me.
Anyway, we didn't close the port hole covers every night (nor did the steward), but we did pull the heavy drapes across them.
Personally, I really don't care for the port holes (although it's better than no view at all). It was like looking thru oversized binoculars.